Google Ads is based on the pay-per-click (PPC) advertising system.
It means you're only charged by Google when someone clicks your ad. In other words, when your ads are running and visible to users without getting clicks you don’t pay anything.
Keep in mind that you have always full control over your maximum advertising costs which is determined by your daily budget. Our article on how do I choose the right daily budget in Google Ads may provide useful insights.